This invention relates to a pointing device in which communication between a patterned passive surface and a movable mouse is established by electrical field coupling, wherein mouse motion on the passive surface creates data signals indicative of the extent and direction of movement.
Pointing devices which are the very general subject of this invention are commonly referred to as "mice". The earliest mouse device was electromechanical, and used a pair of wheels which were rolled across a passive surface to turn potentiometer shafts providing an analog signal related to motion. Improvements included utilizing a single ball as the rolling element, and utilizing optical shaft encoders to detect rotation of the rolling element. Nevertheless, the electromechanical mouse has never been outstandingly reliable. An inherent problem is slippage on the work surface, and it is also difficult to protect the mechanical structures from dirt. Additionally, the electromechanical mouse is expensive to fabricate.
More recently, mouse developments have been directed toward optical design principles, relying on light provided from a source in the mouse body and reflected back from a patterned, passive grid. Optical mice overcome the problem of slippage associate with electromechanical mice, but are limited in application because drawings or papers cannot be interposed between the mouse and the passive mouse surface. In addition, the mouse surface must remain clean to avoid spurious signals.
Thus, there is a need for an improved mouse pointing device.
A pointing device or mouse according to the invention herein comprises a mouse tablet and a mouse movable thereon wherein electrical field coupling is utilized to ascertain movement of the mouse on the mouse tablet. The mouse tablet preferably comprises a repetitive, regular pattern of spaced-apart conductive pixels. The pixels are conveniently provided on a printed circuit board and covered with a thin layer of dielectric material to provide a smooth data surface. The mouse comprises a housing movable on the mouse tablet, the housing containing coupling elements which electrically field couple with the pixels, the degree of coupling depending upon the position of the coupling elements with respect to the pixels. The mouse further comprises circuit means for establishing an electrical field from the coupling elements and means for detecting changes in that field, and such circuit means may be mounted in the mouse housing. When the mouse is moved on the mouse tablet, the coupling elements pass sequentially over the conductive pixels and the non-conductive areas therebetween, position-dependent coupling with the pixels producing output signals indicative of the motion of the mouse.
In accordance with more specific aspects of the invention, two coupling elements are provided for each of the x-axis and y-axis, in order that the direction of mouse motion may be ascertained. The x-axis coupling elements are spaced apart to provide phaseshifted output signals, which can be utilized to ascertain direction of mouse motion in the x-axis. The y-axis coupling elements are also spaced apart to provide phase-shifted outputs for ascertaining direction of y-axis mouse motion. In one embodiment, the pixels may be square and separated from adjacent pixels by the width of the square. Each x-axis coupling element covers a plurality of pixels arrayed in the y-axis, so that movement of the mouse in the y-axis has a negligible effect on coupling with the x-axis coupling elements. The y-axis coupling elements are perpendicular to the x-axis coupling elements, and are also elongated along the x-axis to cover a plurality of pixels.
The coupling elements may each comprise an elongated coil connected in an oscillator circuit. In combination with nonferrous pixels, positioning of the coil over pixels reduces the inductance of the coil, whereby the frequency of the oscillator increases. Thus, the frequency of the oscillator can be monitored to determine mouse movement across the pixels. In combination with ferrous pixels, the frequency of the oscillator decreases over pixels as compared to the frequency of oscillation between the pixels, which also indicates mouse movement. Comparing the voltage across the input and output of the oscillator can also be carried out to derive a signal dependent on the position of the coil with respect to pixels.
The coupling elements may also be elongated conductive strips which comprise one plate of a compacitor. In this embodiment, the mouse housing has mounted therein a conductive guard ring which comprises a plate of a second capacitor sufficiently large to have uniform coupling with the mouse surface independent of mouse position, the guard ring also providing a return path to the coupling element. The mouse tablet, in addition to having conductive pixels, has a conductive backing to complete a coupling loop between the coupling elements and the guard ring. The capacitance between the coupling elements and the mouse surface varies depending upon position of the coupling elements with respect to the conductive pixels. The shape of the capacitance coupling elements are similar to that of the coil coupling elements, i.e. elongated perpendicularly to the axis of interest, and two coupling elements are utilized for each axis in order to ascertain the direction of mouse movement.
In another embodiment, the pixels of the mouse tablet are deployed in strips, one axis having evenly spaced-apart ferrous strips and the other axis having evenly spaced-apart non-ferrous strips. Two coupling element coils are provided for each axis, being spaced-apart to generate phase-shifted output signals in response to mouse movement. The coils for each axis operate at different frequencies wherein the coils are responsive to the pixel material for their respective axes.
The two coupling elements for one axis generate phaseshifted output signals as the mouse is moved in that axis. The out-of-phase output signals from the two coupling elements can be used to generate a digital gray code indicating motion and direction of motion of the mouse on the mouse tablet in the axis, with good resolution. Mouse motion in the other axis is determined from the coupling elements for that axis, in the same manner.
Alternatively, the motion of the mouse on the mouse tablet can be determined by an interpolation method, which includes switching analysis from the output of one coupling element to the out-of-phase output of the other coupling element whenever the output being used to determine mouse motion is at an ambiguity point. Ambiguity points occur where the slope of the output signal changes sign, e.g. when the coupling element is centered over a pixel. At such points, variation in the size of the out-of-phase output signal of the other coupling gives the direction of movement and the size of the signal can be used to derive interpolated motion data. Again, analysis is carried out for each axis.
A pointing device according to the invention is generally utilized with a microprocessor which is used to analyze output signals and derive mouse motion therefrom, and also with a cathode ray tube or similar data display, wherein the output of the pointing device is used to control the position of a cursor dot on the data display, as is known.
It will be noted that the operation of the pointing device does not depend on either a mechanical interface with the mouse surface or an optical interface with the mouse surface wherein materials such as drawings, or the like, can be interposed between the mouse and the mouse tablet without altering its operation. Additionally, the pointing device is highly accurate in that the electrical field coupling between the mouse and the mouse tablet provides a shaped output signal with relatively gradual transition between "on" pixel and "off" pixel positions, whereby the signal can be used to provide information concerning mouse movements in less than the increments of pixel spacing.
Accordingly, it is the principal object of the invention to provide an improved mouse pointing device.
It is an additional object of the invention to provide a mouse pointing device which is highly accurate and responsive to small movements.
It is a further object of the invention to provide a mouse pointing device which operates with drawings or the like on the mouse surface.
It is yet another object of the invention herein to provide a mouse pointing device which is reliable and relatively inexpensive to manufacture.
Other and more specific features and objects of the invention herein will in part be obvious and will in part appear from a perusal of the following description of the preferred embodiments and the claims, taken together with the drawings.